1. Field of the Invention
The present invention relates to the field of industrial fluid fuel fired burners and in particular to swirler mechanisms used in such burners for flame stabilization. Even more particularly, the invention relates to a two component swirler whereby two separate portions of primary gases are swirled separately to stabilize flame while maintaining low NOx levels in burner effluent gases.
2. The State of the Prior Art
The presence of NOx in furnace flue gases is a constant problem facing the burner industry. Many prior inventions and developments in the burner field address this problem by providing various mechanisms and methodologies in an effort to minimize and/or control NOx emissions. In particular it is believed productive to reduce flame temperature, to control flame profile and to combust the fuel with a minimum of excess air so as to minimize the presence of incomplete combustion products, including CO in the furnace flue gases. It is also desirable to make sure that the produced flame is stable and controlled. A known furnace arrangement which employs a swirler in an effort to stabilize and control the produced flame is illustrated and described in co-pending application Ser. No. 09/335,007, filed Jun. 17, 1999 (the xe2x80x9c""007 applicationxe2x80x9d). The ""007 application is owned by the assignee of the present application and the entirety of the disclosure thereof is hereby specifically incorporated herein by reference. The optimization of these various parameters requires tradeoffs, and as a result, the routineers in the burner field constantly seek improvements which will provide relief from a given problem without causing problems somewhere else.
A major and primary object of the invention is to provide for efficient and reliable operation of a burner while minimizing the presence of emissions such as CO and NOx in the flue gas. In particular, the invention provides a novel swirler which provides flame stability and efficiency of operation while minimizing effluent emissions. To this end the invention provides an air swirler structure for an elongated burner having a central axis and concentric primary and secondary air flows moving in a direction generally parallel to said axis. The arrangement is such that the primary air flow is surrounded by the secondary air flow.
The swirler structure includes a first swirler component located in the air flow for swirling the primary air and gas flows. This first swirler component has an outer edge that extends around the axis in radially spaced relationship thereto. The swirler structure also includes a second generally annular swirler component located as well in the air flow for swirling the secondary air flow independently of the swirling of the primary air flow. This second swirler component has an internal edge that extends around the axis in spaced relationship thereto. The diameter of the internal edge of the second swirler component is preferably greater than the outer edge of the first swirler component.
In a preferred form of the invention, the first and second swirler components are arranged in a common plane that extends transversely relative to said axis. Ideally, the swirler components are arranged in a common plane that is perpendicular to the axis. Generally speaking at least the primary air flow comprises a mixture of air and fuel for the burner.
The first swirler component may generally be annular in shape and may have an inner circular edge, and, in a preferred form of the invention, the swirler structure may include a centrally located, elongated cylindrical hub that extends along the burner axis in coaxial relationship thereto. In this form of the invention, the inner circular edge may be disposed in a generally surrounding relationship relative to an outer periphery of said hub.
In a particularly preferred form of the invention, the swirler components may each be generally annular in shape, and the second swirler component may have an outer peripheral rim having a diameter that ranges from about 1.5 to about 1.8 times the diameter of the outer edge of the first swirler component. Preferably the swirler components are arranged to swirl the respective primary and secondary air flows in the same general direction and with essentially the same intensity.
The invention also may provide a burner assemblage comprising an elongated, round burner assembly having a central axis and including internal baffle structure causing concentric primary and secondary air flows to move in a direction generally parallel to said axis, causing the secondary air flow to be generally annular in shape, and causing the secondary air flow to be disposed in generally surrounding relationship relative to the primary air flow. The burner assemblage also may include a swirler structure for swirling the air flow such as has been described above. In a particularly preferred form of the invention, the burner assemblage may comprise a venturi tube arranged to provide swirled flows of primary and secondary air and a surrounding straight flow of tertiary air. Ideally, the burner assemblage may be constructed and arranged to direct a flow of quaternary air around the outside of the venturi tube.
Another embodiment of the invention provides a method for operating an elongated, round burner assembly having a central axis is provided. The method comprises providing a flow of combustion air for the burner assembly and dividing this flow of combustion air into swirled concentric primary and secondary air flows and straight tertiary and quaternary air flows. In accordance with the principles and concepts of the invention, the secondary air flow may generally be annular in shape and the same may be disposed in generally surrounding relationship relative to said primary air flow.
The method also includes a step of causing the primary and secondary air flows to move through the burner assembly in a direction that is generally parallel to the burner axis. In accordance with the method of the invention, the primary air flow is swirled in a first direction at a first swirling intensity and the secondary air flow is swirled independently in a second direction at a second swirling intensity. Ideally, the primary and secondary air flows are independently swirled in essentially the same swirling direction and at essentially the same intensity.